Not much is known about Mercury so far. This is why, in 2013, the European Space Agency ESA plans to launch two space probes that will accurately chart its surface. A diode laser module from Fraunhofer laboratories could be part of the mission.
Mercury – the smallest planet in our solar system and the closest to the sun. We know very little about it at present, other than the information gained from the Mariner 10 probe which paid a visit to the planet a good thirty years ago. Roughly half of the planet’s surface was photographed at that time. In August 2004, NASA sent off the Messenger probe on its journey to Mercury, and the European Space Agency ESA is planning to launch two space probes in 2013. One of the goals of this latest ESA mission, entitled BepiColombo, is to chart the surface of Mercury. Where are craters and escarpments to be found, how deep and how wide are they? A laser altimeter has been designed to make the task easier. It directs a laser beam at the planet’s surface, which reflects the beam back again. From the time taken by the light pulse to cover this distance, it is possible to calculate how far away the surface is. In this way, the experts intend to produce a three-dimensional map.
Under contract to TESAT Spacecom GmbH & Co. KG, researchers at the Fraunhofer Institute for Laser Technology ILT in Aachen have built a prototype of a diode laser pump module to perform this laser charting operation. The module is stable enough to withstand the exertions of the journey and the extreme conditions in space. “The biggest challenge was to make the laser module as light and compact as possible – while producing as great an output as possible,” says Martin Traub, who led the development team at the ILT. The laser module weighs a mere 650 grams and measures only 15 x 5 x 5 centimeters. At 530 watts, the output is quite high as well. If the Fraunhofer researchers win the contract for the space mission, the laser will be made even lighter through the choice of other materials. By way of comparison: These lasers are normally the size of a shoebox and weigh about 5000 grams.
This is not the only challenge: “On Earth, diode lasers of this power class are cooled with water. That is not possible in space, so in our laser module the heat is conducted to the surface of the satellite and radiated from there,” the expert says. Since the diodes of a laser do not work so reliably in a vacuum as under atmospheric pressure, the researchers have designed the laser module in such a way that the outer sheathing can be sealed air-tight. “Tesat is capable of filling such modules with air or other gases and creating an artificial atmosphere inside the laser that remains constant for several years,” states Traub.